Minnesota Plant Life. 177 



shaped appendages which are very sensitive to moisture. These, 

 when dampened, contract around the green spherical spores, 

 hugging them tightly, but as they dry they straighten, loosen- 

 ing the spore-mass in the process. This is why the moistened 

 dust seems more solid than the same dust when dry. The 

 spoon-shaped appendages originate by the splitting of the 

 outer wall of the spore into two ribbons, as if a couple of peel- 

 ings had been removed. An idea of the arrangement can be 

 obtained by imagining the cover of a base-ball unsewed and laid 

 back. The two pieces of cover would then occupy much the 

 same position with reference to the ball as do the four longer 

 and slenderer spoon-shaped appendages with reference to the 

 spore. 



Germination of spores. Although all the spores are of the 

 same size and appearance, yet it is the nature of some of them 

 upon germina- 

 tion to develop 

 little green, 

 prostrate 

 male s, some- 



tlllllP' like Small FIG. 68. Scouring-rush spores; to the left a spore with appendages 

 i 1 i curled up, in moist air; to the right a spore with appendages ex- 



n O r 11 6 Q liver- tended, in dry air. After Atkinson. 



wort plants, 



while others develop females, slightly larger than the males but 

 in general closely resembling them. Both the male and the fe- 

 male scouring-rush plants are provided with leaf-green, emerge 

 from the spores, strike their root-hairs into the soil and lead 

 an independent existence. The males produce microscopic 

 spherical spermaries in which arise spermatozoids with large 

 numbers of swimming threads. The females produce a few 

 egg-organs of the characteristic bottle-shape, at the bottom of 

 each of which a single egg is formed. After the fecundation of 

 the egg during rains, or when in some other way plenty of 

 water is available as a medium for the locomotion of the sperms, 

 the embryo of the scouring-rush begins to grow very much 

 as did that of the fern. An erect stem is first produced, then 

 from its base a rootstock. If at the end of the year the erect 

 stem dies, buds on the rootstock remain to form the stems of 

 the succeeding year. By means of its underground stem the 

 13 



